Our goal is to elucidate the transcriptional specialization of human high endothelial venules (HEV), unique post-capillary venules that control lymphocyte homing and thus immune and inflammatory responses. Most studies of HEV, and the only comprehensive studies of gene expression by HEV, have been carried out in mice: relatively little is known about human HEV or indeed, about the gene programs underlying the segmental and tissue specialization of blood endothelial cells in man. Notably, several vascular molecules implicated in lymphocyte homing in the mouse, including the peripheral lymph node addressin, VAP1, CCL21 and others, are regulated differently in humans. We recently completed comprehensive transcriptomic studies of mouse lymphoid tissue high endothelial cells (HEC) and enriched capillary EC (CAP). Here we shall apply our established protocols to perform whole genome expression analyses of human lymphoid tissue HEV and CAP. Aims include: 1) To perform whole genome expression profiling of high endothelial cells (HEC) and capillary endothelial cells (CAP) from human tonsils, adenoids, peripheral lymph nodes (PLN), and appendix. We will apply existing protocols for endothelial dissociation from fresh human lymphoid tissues, and will purify HEC and capillary EC using FACS cell sorting protocols with established HEC and pan-EC markers. RNA will be submitted for whole genome expression profiling. 2) To define the segmental (HEV vs CAP) and tissue-specific (tonsil or adenoid, PLN, appendix) transcriptional specialization of human high endothelial cells (HEC). We shall elucidate vascular programs that define HEC specialization (and thus lymphocyte homing) by comparing the transcriptomes of HEC and of capillary endothelium (CAP), which unlike HEC inhibit leukocyte adhesion. We will also identify gene sets expressed in HEC in a tissue-specific fashion, genes likely to encode mechanisms that control vascular addressins or chemo attractants for tissue-specific lymphocyte recruitment. 3) To compare and contrast human vs. mouse HEV-, CAP- and tissue-specific HEC gene signatures, and to identify evolutionarily conserved transcriptional programs of HEC. We shall define differences in HEC gene expression in humans vs. mice, the most studied animal model. We will identify genes with conserved patterns of HEC vs CAP, or of tissue-specific HEC expression: such genes are likely to encode molecular mechanisms (transcription factors, adhesion or attractant molecules, signaling pathways) critical to HEV function. Comprehensive analyses of human HEV and capillary EC transcriptomes will open up new areas of investigation in vascular biology and immunology, and will inform efforts to translate mouse studies to the clinical arena. The data generated will constitute a valuable resource for elucidation of mechanisms of vascular control of lymphocyte recruitment, and may lead to novel targets and approaches for the control of autoimmune and other pathologic inflammatory disorders.